A liquid crystal display device has been currently used in, for example, a notebook personal computer, a monitor for a desktop personal computer, a portable digital assistant, or a television by taking advantageous feature such as being thin, light weight, and low power consumption.
The liquid crystal display device originally involves such a problem that its display quality deteriorates in a viewing angle direction. The problem derives from the principle of the liquid crystal display device. The principle of the liquid crystal display device is generally as described below.
That is, the alignment states of the liquid crystal molecules of a driving liquid crystal medium interposed between two substrates each provided with an electrode and an alignment layer are changed by a voltage to be applied to the medium, and then a retardation to be expressed changes depending on the alignment states of these liquid crystal molecules. Further, polarized light entered onto the driving liquid crystal medium from a light source through a polarizer is changed into another polarization state by a retardation to be expressed by the alignment state of each of the liquid crystal molecules upon passing of the driving liquid crystal medium. The quantity in which the light that has passed the driving liquid crystal medium passes a polarizer placed on an observer side changes depending on the changed polarization state.
That is, arbitrarily changing the voltage to be applied to the driving liquid crystal medium controls the quantity of the light that passes the polarizer on the observer side. We acknowledge a combination of a plurality of pixels in each of which the quantity of the light that passes the polarizer on the observer side is controlled as display.
The following two factors are given as factors responsible for the deterioration of the display quality of the liquid crystal display device in the viewing angle direction. One of the factors is that a retardation to be expressed by the driving liquid crystal medium is changed not only by the alignment state of a liquid crystal molecule but also by the direction of light to be entered, that is, the direction in which an observer observes the liquid crystal display device. The other is that an angle formed between the absorption axes of the respective polarizers placed on an incidence side and an emission side changes depending on the direction in which the observer views.
A concept and an approach concerning optical compensation with a retardation film having a specific optical characteristic have been proposed for alleviating the deterioration of the display quality in the viewing angle direction caused by those factors (see, for example, Non Patent Literature 1 and Non Patent Literature 2).
Most of the retardation films have been currently obtained by stretching thermoplastic resins typified by a polycarbonate-based resin and a cyclic olefin-based resin. However, in order to provide a specific optical characteristic to a large area of a retardation film uniformly, a special technology and complicated steps are needed.
A liquid crystal display device optically compensated with a retardation film based on a film in which a liquid crystal is immobilized in a predetermined alignment state has been proposed as a technology that replaces the foregoing (see, for example, Patent Literatures 1 to 4). In this film, a composition containing liquid crystal molecules each provided with a polymerizable functional group (which may hereinafter be referred to as “polymerizable liquid crystal material”) is utilized for immobilizing its alignment. A retardation film based on the polymerizable liquid crystal material has, for example, the following advantage. The film can be thinned as compared with the case where a thermoplastic resin is stretched.
However, when the retardation film based on the polymerizable liquid crystal material is actually produced, even any such approach requires that an alignment layer provided with an anchoring energy by being subjected to a rubbing treatment or irradiation with polarized ultraviolet light be provided for uniformly aligning the polymerizable liquid crystal material. Accordingly, a material and a production step for the film are separately needed. In addition, the performance of proper optical compensation typically requires a plurality of retardation films different from each other in the alignment state of a liquid crystal or in thickness, and hence the production steps become additionally complicated. Therefore, an approach with an additionally small production load has been requested for the mass production of such retardation film or a liquid crystal display device having the retardation film.